100 AGRICULTURAL BACTERIOLOGY 



were thus prepared. The Chinese are still using the pro- 

 cess. Nitrates can also be obtained by the leaching of the 

 soil to which large quantities of organic matter have been 

 added and which has been protected from leaching. Dur- 

 ing the Civil War the Confederate States were forced to 

 leach the soil beneath old tobacco barns. The Chinese re- 

 move the dirt floors from their houses and dissolve the ni- 

 trate that has there accumulated. 



Many of the characteristics of the change of ammonia 

 to nitric acid in the soil related the process to a biological 

 cause. The causal bacteria were isolated by Winogradsky 

 in 1889. He confirmed earlier observations that the change 

 of ammonia to nitric acid is not a single chemical change, 

 but involves two steps: the ammonia is first oxidized to 

 nitrous acid, and this substance further oxidized to nitric 

 acid. Winogradsky isolated two groups of bacteria con- 

 cerned in these changes. The first could grow only when 

 ammonia was available to it. This compound represented 

 the sole source of energy and of nitrogen for the organism. 

 The second group was limited to the nitrous acid formed by 

 the first for its energy and nitrogen. The change of am- 

 monia to nitric acid is an example of metabiosis. The acids 

 formed, of course, unite with bases to form neutral salts, 

 nitrites, and nitrates. 



The nitrous acid-forming bacteria differ in their mor- 

 phology in various parts of the world, but apparently all are 

 invested with the same peculiar physiological characteris- 

 tics. Earlier it was thought that the presence of chlorophyl 

 was essential for the use of carbon-dioxide as a source of 

 carbon, and that no other type of life than the green plant 

 was able to utilize so stable a substance as carbon-dioxide. 

 The nitrifying bacteria are able to grow in the total absence 

 of carbon, except in the form of carbon-dioxide. Wino- 

 gradsky showed that the energy needed for the process is 



